The source "Applied Optics", Vol. 16, no. 7, July 1977, pp. 1966-1970, discloses an assembly having the features described in paragraph 1 of the "Technical field of the invention" above. This source (see in FIG. 5 on p. 1968) describes a specially designed carrier element for coupling a semiconductor laser, e.g. a GaAs diode, and an optical fiber having a circular cross section, said element simultaneously carrying the cylinder lens for coupling the laser radiation produced by the GaAs diode into the subsequent optical fiber. This substantially cylindrical carrier element is provided on the top with a given number of V-groove recesses which are preshaped by mechanical, i.e. metal-removing, processing of the carrier element material, e.g. copper, in accordance with the intended coupling between laser, cylinder lens and optical fiber and in order to guarantee the necessary optical adjustment of these elements to one other. Due to this design of the carrier element the optical elements subsequent to the GaAs diode, i.e. the cylinder lens and the optical fiber, can be inserted into these above-mentioned recesses, the mutual adjustment of these elements being dependent on the precision with which the corresponding recesses have been machined in the carrier element. Very low tolerances are of course permissible here to allow for the necessary ultimate adjustment.
The mechanical requirements for the tolerances of such a carrier element, and in particular the required positioning accuracy for the GaAs diode relative to the subsequent optical elements, are thus extremely high since particularly this laser diode must be applied and fastened to the surface of the carrier element, for example by gluing or soldering. This means that the production and processing of such a carrier element is very elaborate to permit the necessarily very low tolerances to be met.
This known assembly is intended to focus as much as possible of the radiation emitted by one semiconductor diode into the core of the optical fiber,e.g. a multimode fiber with a circular cross section. There is no intention here to provide a laser module with the greatest possible power and radiation quality.
Further, "Applied Optics", Vol. 17, No. 3, 1978, p. 479 ff., discloses an assembly wherein each individual laser of a monolithic laser diode array is coupled by means of a common cylinder lens to a great number of individual optical fibers. A carrier element in the form of a silicon substrate is likewise used here, a given number of V-shaped recesses being preshaped in this silicon substrate in accordance with the intended arrangement of cylinder lens and optical fibers for coupling between a laser diode and an optical fiber as in the known coupling assembly explained above.
Extremely low process tolerances are also permissible in this case. In addition, the direct contact between cylinder lens and laser diode array can drastically change the properties of the individual laser diodes, i.e. the laser diodes can very easily be mechanically destroyed when the cylinder lens is inserted into the V-shaped groove provided in the silicon substrate. In this latter assembly the manufacturing expenditure is therefore likewise considerable.